Did all that drinking you did in college really hurt your grades?

Yeah, it did. Especially if you were smart:

This paper examines the effect of alcohol consumption on student achievement by exploiting the discontinuity in drinking at age 21 at a college in which the minimum legal drinking age is strictly enforced. We find that drinking causes significant reductions in academic performance, particularly for the highest-performing students. This suggests that the negative consequences of alcohol consumption extend beyond the narrow segment of the population at risk of more severe, low-frequency, outcomes. Thus, our results indicate policies that combat drinking—particularly binge drinking that occurs around age 21—may well have large positive effects that are broader than previously known.